It is well known in the field of spark ignited gasoline engines, particularly those for automotive use, to provide means for heating the intake air-fuel mixture with heat transferred from the engine exhaust gases. The heat provided warms the induction system and aids vaporization of fuel in the intake mixture, thus assisting proper distribution of the mixture to the various cylinders and improving combustion in the combustion chambers.
Many such systems have utilized juxtaposed intake and exhaust manifold arrangements wherein exhaust gases are directed against a plate or wall to which the intake manifold mixture is exposed, preferably at a point below the carburetor throat or inlet passage. The heating of the plate or wall by exhaust gases vaporizes fuel droplets impinging on the wall or plate and heats the adjacent air-fuel mixture. Control of heat transfer in such systems is generally provided by an exhaust gas diversion valve, mechanically actuated by a thermostatic, or time controlled, mechanism that provides maximum exhaust heat during the engine warm up period and substantially reduces or cuts off the heat when normal operating conditions have been reached.